Forming coil

ABSTRACT

Magnetic forming apparatus is described in which a conductive forming coil is formed in a generally cylindrical single turn, and wherein a pair of generally parallel flat conductors are connected to the adjacent ends of the coil and extend axially of the coil.

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milemll [151 3,6MA1W 1 *ll elha, 2.21, 1 1 72 [54] EURMHNG (IQ/11L [72] Inventors: Hansiorg Jansen, La 1011a; Paul Wildii James A. Kline, both of San Diego, all of Calif.

[73] Assignee: Gull @il Emmi-anion Notice: The portion of the term of this patent subsequent to Feb, 18, 1986, has been disclaimed.

[22] Filed: Dec. 9 113613 [21] Appl. No: 762,383

[52] 111.6. C1 ..72/56 [5]] 11m. ([11 ..nzm 26/1141 [58] Field of earcli ..72/56; 336/225, 229,232

[56] llieierencei: Cit/call UNlTED STATES PATENTS 3,108,325 10/1963 lllarvey et a1 ..18/165 3,167,043 1/1965 Forth ..72/56 3,258,573 6/1966 Morin et a1. ..2l9/9.5

3,256,846 6/1966 lieinanen 1 13/120 3,321,946 5/1967 Ferguson ..72/56 3,372,566 3/1968 Schenk et a1 ...72/56 3,383,890 5/1968 Wildi ...72/56 3,427,842 2/1969 Jansen ..72/56 OTHER PUBLICATIONS 11110chgeschwindigkeitsbearbeitung Ill by G. Weimar; pp. 893, 894 of Werkstatt & Betrieb, 1963.

Primary Examiner-Richard J. Herbst Attorney-Fitch, Even, 'labin & Luedelca Magnetic forming apparatus is described in which a conduc tive forming coil is formed in a generally cylindrical single turn, and wherein a. pair of generally parallel flat conductors are connected to the adjacent ends of the coil and extend axi ally of the coil.

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'TTVS.

I UlitII IING CGIL This invention relates to magnetic forming apparatus and, more particularly, to improved magnetic forming apparatus which is particularly adapted for producing expansion type deformation in regions of relatively short axial size.

Apparatus has been developed for forming materials by employing varying magnetic fields of high intensity. An example of such apparatus is shown and described in the US. Pat. No. 2,976,907, issued Mar. 28, 196i, and assigned to the assignee of the present invention. In apparatus of this general type, an electric current pulse of high amperage is passed through a coil to provide a desired magnetic field of high intensity. The current pulse may be applied to the coil directly from a current pulse source. A conductive workpiece positioned in the pulsed magnetic field produced by the coil has a current pulse induced in it. This current pulse interacts with the pulsed mag netic field to produce a force acting on the workpiece. If the force is sufficiently strong, a deformation of the workpiece results. The shape of the deformation is dependent upon the distribution, in time and space, of the magnetic field, and the position of the workpiece relative to the field. Repeated pulses of current may be applied to the coil, thus causing a series of deforming impulses to act upon the workpiece.

Magnetic forming apparatus for producing expansion type deformation of cylindrical workpieces has heretofore typically incorporated helical magnetic forming coils. Such coils are generally comprised of a strong conductor having a round, rectangular or other convenient cross section wound on a mandrel of a mechanically strong and electrically insulating material. The pitch of the helical coil is selected in accordance with the size of the conductor and the necessary separation between adjacent turns of the helical coil. The conductor is returned axially through the center of the helix in order to position the ends of the coil adjacent each other for convenience in supplying current pulses thereto.

The coil construction described above is well suited for expanding a cylindrical workpiece in a region which is long relative to the pitch of the coil. If the region to be expanded is to be very short axially relative to the pitch of the helical coil, this type of coil construction may be unsatisfactory since there are practical limitations on the minimum pitch of the helix with which the coil can be constructed. If the number of turns is reduced, the nature of a helical coil is such as to render the coil correspondingly weaker. The reason for this is that forces acting on the coil radially inward with respect to the helix (such forces are produced during the magnetic forming operation) cause a twisting type of deformation of the helical coil. This may be understood by visualizing a single loop segment of the helix. Pressure acting along the circumference of the loop tends to push the theoretical ends of the loop past each other, any resistance thereby being derived only from the coil body itself. Although the supporting mandrel may offer some resistance to deformation of the coil, typical insulating materials utilized for mandrels have some degree of deformation under compression. Repeated or excessive deformation of the coil can cause damage to both the coil and the supporting mandrel.

Accordingly, it is an object of the present invention to provide improved magnetic forming apparatus.

Another object of the invention is to provide improved magnetic forming apparatus particularly suited for producing expansion type deformation in regions of relatively short axial size.

Another object of the invention is to provide magnetic forming apparatus utilizing a coil construction which overcomes many of the shortcomings of a helical-type coil.

Other objects of the invention will become apparent to those skilled in the art from the following description, taken in connection with the accompanying drawings wherein:

FIG. I is a perspective view of apparatus constructed in accordance with the invention;

FIG. 2 is a top view of magnetic forming apparatus including the structure illustrated in FIG. I and additional elements assembled therewith;

FIG. 3 is a side elevational view of the apparatus of FIG. 2;

FIG. A is an end view, partially in section, of the apparatus of FIGS. 2 and 3;

FIG. 5 is a perspective view of an additional embodiment of the invention; and

FIG. 6 is a full section end view of the apparatus of FIG. 9".

Very generally, the magnetic forming apparatus of the invention comprises a conductive coil responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field to expand a tubular workpiece disposed in the field surrounding the periphery of the coil. The coil is formed in a generally cylindrical single turn having ends aligned and adjacent each other. A pair of flat conductors extend generally parallel to the axis of the coil. At least a portion of each conductor is positioned within the periphery of the coil to clear the workpiece and thus enable the coil to be positioned a substantial distance inside the workpiece. The con ductors are connected to the ends of the coil, respectively, for conducting current pulses to and from the coil.

Referring now more particularly to FIG. I, the coil Ill illus trated therein comprises a bar of rectangular cross section formed in a generally cylindrical single: turn. The ends I2 and I3 of the coil II are positioned adjacent each other. Highenergy current pulses are supplied to the coil II by means, subsequently described, causing the coil to produce a magnetic field. A cylindrical workpiece, not illustrated, is disposed about the coil II coaxial therewith and spaced therefrom. The workpiece has a current induced therein by the magnetic field. Magnetic pressure is built up on the opposing surfaces of the coil and the workpiece, causing the workpiece to be deformed radially outward. If desired, a die, not shown, may be disposed about the outer surface of the workpiece, such die having a cavity into which the deformation occurs.

In order to conduct electrical current pulses to and from the coil Ii, a pair of flat conductors M and 116 are provided. The conductors are separated from each other by means subsequently described and are disposed generally parallel with the axis of the coil. The conductor M has a narrowed portion 17 positioned within the periphery of the coil and connected at one edge to the end 112 of the coil. Similarly, the conductor 116 has a narrowed portion 11% positioned within the periphery of the coil and connected at one edge to the end I3 of the coil. The conductors IA and 16 not only provide means for carrying current to and from the coil, but act to support the coil as well. The lower edges of the conductors I4 and 116 are provided with outwardly extending flanges I9 and 2I, respectively, for bolting the conductors to a suitable source (not shown) of current pulses, such as a pair of transformer terminal plates or a pair of bus bars.

Other elements of the magnetic forming apparatus associated with the elements just described in connection with FIG. 1 have not been illustrated in FIG. I for clarity. Such other elements may be seen, however, in FIGS. 2 through A in their assembled relation with the items shown in FIG. I. A layer 22 of a pressure resistant electrical insulation material, such as epoxy fiber glass, is disposed between the conductors I4 and I6 and is shaped to conform with the narrowed portions i7 and 18 thereof. The insulation separates the conductors electrically and also prevents them from being forced together to contact each other. The insulation layer 22 also includes a portion extending between the ends 112 and I3 of the coil II to prevent contact therebetween. Accordingly, forces exerted on the coil and extending radially inwardare resisted by the coil and the insulation between the ends 112 and 113. Moreover, the stresses placed upon the coil during the exertion of such forces are primarily compressive stresses exerted circumferentially around the coil. In addition, the axial dimension of the coil may be made quite small, for forming regions of correspondingly small axial size.

The conductors M and 116 are made the full width of the terminals to which the flanges I9 and 211 are attached for as long a distance as possible (depending upon how far into the workpiece the coil llll is to be inserted). By doing so, the inductance of the conductors is minimized, as well as is the magnetic force tending to push the conductors apart. For accommodating the workpiece, the conductors, as previously mentioned, are narrowed in the portions 17 and 18, the length of the narrowed portions depending upon the location of the region of the workpiece to be expanded.

In order to contain the force which tends to push the conductors 14 and 16 apart when current pulses are conducted, the conductors 14 and 16 are clamped together near the upper edges of their widened portions by a pair of straps 23 and 24. The straps 23 and 24 are disposed on opposite sides of the conductor-insulation sandwich and are held together by bolts 26 insulated by sleeves 27 of insulating material passing through suitable openings provided in the straps and in the conductors. The heads of the bolts bear against metal washers 29 which are insulated from the strap 23 by washers 31 of insulating material. A similar arrangement, not illustrated, is provided at the opposite end of the bolts 26 upon which nuts, also not illustrated, are threaded. The clamping force of the straps 23 and 24 help to prevent the conductors 14 and 16 from separating.

In the region of the narrowed portions 17 and 18, the force tending to push the conductors apart is increased an amount corresponding to the smaller facing areas. As insurance against separation of the narrowed portions 17 and 18, a fitted insert 32 of insulation material is disposed within the space betweenthe coil 11 and the narrowed portions 17 and 18 of the conductors 14 and 16, respectively. This helps to resist movement of the narrowed portions 17 and 18 outwardly toward the coil 11. To provide further rigidity to the assembly, the insert 32, which extends above and below the coil 11, is wrapped with a plurality of prestressed epoxy impregnated glass filaments 30. Such filaments have a tensile strength of the same order of magnitude as many metals, imparting great strength to the assembly.

The insulating insert 32 is provided with a flange 33 extending outwardly about the top thereof. The outer diameter of the flange 33 is equal to the outer diameter of the coil 11. An annular insert 34 having an annular recess 36 therein fits around the lower edge of the insert 32. The recess 36 accommodates a plurality of epoxy-impregnated glass filaments 35 wound on the insert 34 in the same manner and for the same reason as the filaments 30. The outer diameter of the annular insert 34 is equal to the outer diameter of the coil 1 1 and the flange 33. A sleeve 38 of a suitable insulating material is slipped over the flange 33, the fiber glass strands 30, the coil 11, the fiber glass filaments 35 and the insert 34 to protect the outer surface of the assembly. An inwardly extending annular shoulder 39 seats on the top of the flange 33 and locates and positions the sleeve 38.

During the passage of current pulses through the coil during forming operations, some heat is produced due to ohmic losses. In order to remove such heat, provision is made for cooling the coil 11. A coolant tube 41 is provided recessed in a trench formed in the coil itself. The coolant tube is in contact with the coil in the trench, and may be secured in place by any suitable means, such as by brazing or spot welding. The trench may be closed by fabricating the coil in two parts. The portions of the tube outside the trench in the coil 11 are designated as sections 42 and 43. The tube section 42 extends upwardly alongside the conductor 14 in contact therewith, and is bent in a generally U-shape near the top of the conductor. The tube section 42 then extends down to the trench near the end 12 of the coil 1 1. Similarly, the tube section 43 passes upwardly alongside the conductor 16 in contact therewith, is bent over near the top of the conductor in a generally U- shaped configuration, and extends down to the trench near the end 13 of the coil 11. The tube sections 42 and 43 are secured to the conductors l4 and 16, respectively, by suitable means such as brazing. By running the tube sections 42 and 43 in the regions just described, the tube is protected from mechanical deterioration, since such regions are of only moderate magnetic pressure, thus minimizing the forces to which the tube sections are subjected.

The lower end of the tube section 43 of the tube 41 terminates in a hole 44 bored in the strap 24. The tube passes through a suitable opening provided in the strap 24 communicating with the hole 44. A fluid connection, not illustrated, is made to the hole 44 to supply cooling fluid to the tube 41. The tube section 42 terminates, at its lower end, in a similar arrangement, not shown, through which the coolant is returned to its source for cooling and recirculation.

Referring now to FIGS. 5 and 6, a further embodiment of the invention is illustrated. Parts therein having functions similar to the parts in the previously described embodiment have been given identical reference numbers preceded by a one. Thus, the coil 111 is supported on a pair of conductors 114 and 116 having narrowed portions 117 and 118, respectively, positioned within the periphery of the coil. The conductors extend axially of the coil and the narrowed portions are secured to the coil at the ends 112 and 113 thereof. A layer 122 of insulation is positioned between the ends 112 and 113 of the coil 11] and between the conductors 114 and 116.

The design of the apparatus in FIGS. 5 and 6 is suitable for positioning the coil 111 deep inside a cylindrical workpiece, such as may be desirable for producing a bulge relatively deep inside a tube. In this case, rather than continuing the conductors 114 and 116 over the necessary length, the conductors are terminated in a pair of coaxial cylindrical conductors 151 and 152, respectively. The cylindrical conductor 151 has a web 153 closing its end, and the conductor 114 is suitably secured thereto, such as by welding. Similarly, the conductor 152 has one end half closed by a web 154 (thus allowing clearance for passage of the conductor 114) to which the conductor 116 is suitably secured, such as by welding. A sleeve 156 of insulation is positioned between the cylindrical conductors 151 and 152 to provide electrical separation thereof, and a layer 157 of insulation is positioned between the web 154 and the web 153. The outer diameter of the cylindrical conductor 152 is about equal to the outer diameter of the coil and is slightly less than the inner diameter of the tube to be formed, thus allowing the apparatus to pass within the tube to the desired depth. The associated reinforcing elements, which are not shown in FIGS. 5 and 6, may be essentially the same as those illustrated in connection with the previous embodiment. Because of the coaxial arrangement of the conductors, the inductance is minimized, since it is well known that a coaxial conductor consisting of two tubes with intermediate insulation represents a very low inductance electrical connection. The inductance is essentially determined by the thickness of the insulation and the diameter of the tubes.

It may therefore be seen that the invention provides improved magnetic forming apparatus which is well suited for expanding workpieces in regions of relatively short axial length. By constructing a coil in accordance with the invention, it is possible to provide substantial cross section in the coil itself for added strength without reducing the available area for flux return through the inside of the coil. Thus, high magnetic efficiency may be retained along with high structural rigidity. Connections to the coil may be made so that they have very little inductance and do not appreciably restrict the return path for flux through the middle of the coil. The coil may be readily fabricated and is easily adapted for a variety of expansion forming operations.

Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

We claim:

1. Magnetic forming apparatus comprising, a conductive coil responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field to expand a tubular workpiece disposed surrounding the periphery of said coil, said coil having a single turn of generally cylindrical configuration with ends aligned and adjacent each other, and having an internal aperture, a pair of flat conductors projecting HIM into said aperture and supporting said coil ends against inward movement into said aperture and extending generally parallel to the axis of said coil and being connected to the ends of said coil, respectively, for conducting current pulses to and from said coil,,at least a portion of each of said conductors being positioned entirely within the periphery of said coil to clear the workpiece and being of sufficient length to position said coil within the workpiece, and connecting means on said conductors at the ends thereof opposite said coil for connecting said conductors to a source of current pulses and for mechanically securing said conductors for supporting said coil.

2. Magnetic forming apparatus according to claim ll including insulating means positioned between the adjacent ends of said coil for preventing contact therebetween.

3. Magnetic forming apparatus according to claim ll including insulating means positioned between said flat conductors, and further including means for clamping both said fiat conductors toward each other against said insulating means.

4. Magnetic forming apparatus according to claim 3 including a plurality of epoxy-impregnated glass filaments wrapped around the outer periphery of said coil to prestress said conductors toward each other against said insulating means.

5. Magnetic forming apparatus according to claim 3 including a pair of shaped inserts of compression resistant insulating material disposed between each of said conductors and said coil.

6. Magnetic forming apparatus according to claim ll including a coolant passage internally of said coil, coolant supplying means and coolant receiving means disposed toward the ends of said conductors opposite said coil, a first coolant tube portion secured against one of said conductors and extending therealong from one end of said coolant passage to said coolant supplying means, and a second coolant tube portion secured against the other of said conductors and extending therealong from the other end of said coolant passage to said coolant receiving means.

7. Magnetic forming apparatus according to claim l includ ing an elongated tubular electrically conductive first support secured to one of said conductors and supporting same, and an elongated tubular electrically conductive second support secured to the other of said conductors and supporting same, said first and second supports being secured to said conductors, respectively, at the ends of said conductors opposite said coil and being disposed coaxially and spaced from each other in axial alignment with said coil, the outer diameter of the outermost one of said supports being no greater than the outer diameter of said coil. 

1. Magnetic forming apparatus comprising, a conductive coil responsive to pulses of electrical energy applied thereto to conduct a current for producing a magnetic field to expand a tubular workpiece disposed surrounding the periphery of said coil, said coil having a single turn of generally cylindrical configuration with ends aligned and adjacent each other, and having an internal aperture, a pair of flat conductors projecting into said aperture and supporting said coil ends against inward movement into said aperture and extending generally parallel to the axis of said coil and being connected to the ends of said coil, respectively, for conducting current pulses to and from said coil, at least a portion of each of said conductors being positioned entirely within the periphery of said coil to clear the workpiece and being of sufficient length to position said coil within the workpiece, and connecting means on said conductors at the ends thereof opposite said coil for connecting said conductors to a source of current pulses and for mechanically securing said conductors for supporting said coil.
 2. Magnetic forming apparatus according to claim 1 including insulating means positioned between the adjacent ends of said coil for preventing contact therebetween.
 3. Magnetic forming apparatus according to claim 1 including insulating means positioned between said flat conductors, and further including means for clamping both said flat conductors toward each other against said insulating means.
 4. Magnetic forming apparatus according to claim 3 including a plurality of epoxy-impregnated glass filaments wrapped around the outer periphery of said coil to prestress said conductors toward each other against said insulating means.
 5. Magnetic forming apparatus according to claim 3 including a pair of shaped inserts of compression resistant insulating material disposed between each of said conductors and said coil.
 6. Magnetic forming apparatus according to claim 1 including a coolant passage internally of said coil, coolant supplying means and Coolant receiving means disposed toward the ends of said conductors opposite said coil, a first coolant tube portion secured against one of said conductors and extending therealong from one end of said coolant passage to said coolant supplying means, and a second coolant tube portion secured against the other of said conductors and extending therealong from the other end of said coolant passage to said coolant receiving means.
 7. Magnetic forming apparatus according to claim 1 including an elongated tubular electrically conductive first support secured to one of said conductors and supporting same, and an elongated tubular electrically conductive second support secured to the other of said conductors and supporting same, said first and second supports being secured to said conductors, respectively, at the ends of said conductors opposite said coil and being disposed coaxially and spaced from each other in axial alignment with said coil, the outer diameter of the outermost one of said supports being no greater than the outer diameter of said coil. 